This article by James M. Giffen, MD and Lisa D. Carlson DVM was excerpted by permission from

Hip dysplasia is the most common cause of rear leg lameness in dogs. The highest incidence occurs in large-breed dogs, including Saint Bernards, Newfoundlands, Rottweilers, Chesapeake Bay Retrievers, Golden Retrievers, German Shepherd Dogs and many others. Smaller breeds are also affected, but are less likely to show symptoms. According to statistics compiled by the Orthopedic Foundation for Animals, the risk of hip dysplasia in many of the large-breed dogs presented to them for certification over the last 25 years ranged from 20 to 40 percent.

Hip dysplasia is a polygenic trait. That is, more than one gene controls the inheritance. The hip is a ball-and-socket joint; the ball is the head of the femur and the socket is the acetabulum of the pelvis. In a dysplastic hip, the head of the femur fits loosely into a poorly developed, shallow acetabulum. Joint instability occurs as muscle development lags behind the rate of skeletal growth. As the stress of weight bearing exceeds the strength limits of the supporting connective tissue and muscle, the joint becomes loose and unstable. This allows for free play of the femoral head in the acetabulum, which promotes abnormal wear and tear.

Feeding a very high-calorie diet to growing dogs can exacerbate a predisposition to hip dysplasia, because the rapid weight gain places increased stress on the hips. Being overweight supports the genetic potential for hip dysplasia, as well as other skeletal diseases. Another factor that can bring on the symptoms of hip dysplasia is inappropriate exercise during the period of rapid bone growth.

Young dogs should be discouraged from jumping up and down from heights and from standing up on their back legs (which dogs do when they stand up against a fence or window to get a better view).

Dogs with hip dysplasia are born with hips that appear normal but progressively undergo structural changes. The age of onset is 4 to 12 months. Affected puppies may show pain in the hip, walk with a limp or a swaying gait, bunny hop when running and experience difficulty in the hindquarters when getting up. Pressing on the rump can cause the pelvis to drop. With the puppy on its back, the rear legs may not extend into the frog-leg position without causing pain.

An X-ray of the hips and pelvis is the only reliable way of determining whether a dog has hip dysplasia. Good X-rays require heavy sedation or anesthesia. The standard view is taken with the dog lying on his back with his rear legs parallel and extended. The knees (stifles) are rotated internally. Care is taken to be sure that the pelvis is not tilted.

Hip dysplasia is graded according to the severity of X-ray findings. With normal hips (graded excellent), the femoral head fits tightly into a well-formed hip socket with a minimum of space between the head of the femur and the acetabulum. The hip ball is almost completely covered by the socket. With mild hip dysplasia, the X-rays will show mild subluxation (increased space in the joint) with the hip ball partway out of the socket. There are no changes associated with degenerative arthritis.

In moderate dysplasia the hip ball is barely seated into a shallow acetabulum. Arthritic changes begin to appear. These include wear and flattening of the femoral head, a rough appearance to the joint surfaces and the beginning of bone spurs. In severe dysplasia the head of the femur is completely out of the joint and arthritic changes are marked.

Once arthritis is noted, the condition is irreversible. But even with arthritis, some dogs are not lame. The onset of lameness is unpredictable, and some dogs may go most of their lives with dysplastic hips but no lameness. Others develop lameness as puppies.

The OFA provides a hip dysplasia registry for purebred dogs. For a nominal fee, an OFA-certified radiologist will review hip X-rays taken by your veterinarian and, if the conformation of the hips is normal for the breed, certify the dog by assigning it an OFA number. As an optional step, you can have the OFA number added to your dog's AKC registration papers.

Dogs must be 24 months of age or older to be certified. Some female dogs will show subluxation when X-rayed around an estrus cycle, so OFA recommends not X-raying females around a heat period or within three to four weeks of weaning a litter.

The OFA registry is closed. That means if the dog is found to have hip dysplasia, the information remains confidential.

Dog breeders often request preliminary evaluations on hip status before selecting puppies for show and breeding stock. The OFA accepts preliminary X-rays on puppies as young as four months of age. Their own analysis reveals that these evaluations are about 90 percent accurate when compared with follow-ups at 24 months of age.

Another method of evaluating hips was developed at the University of Pennsylvania Veterinary School and is now administered by PennHip. PennHip X-rays are taken in a different position than X-rays for OFA certification. They are used to gauge joint laxity, which can be measured in puppies, starting at 16 weeks of age. The joint laxity does not change as the dog ages.

Dogs X-rayed for PennHip measurements are compared only to other dogs of the same breed. Your dog then receives a joint laxity distraction index (DI) number. PennHip suggests that only dogs in the top half for their breed with respect to joint laxity (that is, those with the tightest joints) should be used for breeding. Those dogs that fall into the lower half, which are the ones with the loosest hips, have a greater chance of developing hip dysplasia in the future.

Finally another organization, the Institute for Genetic Disease Control in Animals, also maintains a hip dysplasia registry. The GDC certifies dogs starting at 12 months of age. The GDC's registry is open. That is, the GDC provides information on affected as well as normal dogs to anyone making an inquiry.

The GDC requests that veterinarians palpate the stifle joints for patella luxation at the time of hip X-rays. They also request that copies of pedigrees be submitted with X-rays. The goal of the GDC is to build a large integrated database on the orthopedic conditions it registers.

A genetic test for hip dysplasia applicable for a number of breeds is under development through VetGen.

Treatment:

Treatment of hip dysplasia is both medical and surgical. Medical treatment includes restricting activity and giving a NSAID analgesic such as Rimadyl, and a joint chondroprotectant such as Adequan to relieve pain and inflammation and to repair damaged cartilage.

It is important to exercise lame dogs on a leash and not allow them to run, jump or play as long as they exhibit pain. Swimming is an excellent exercise that improves muscle mass and joint flexibility without overstressing the hips. Feed a quality food in amounts appropriate for normal (but not accelerated) growth. Overweight puppies should be given a calorie-restricted diet. Discuss this with your veterinarian. Vitamin and mineral supplements have no proven benefit in preventing or treating hip dysplasia, and may even be detrimental if given in excess.

After reviewing the X-rays, your veterinarian may recommend hip surgery. Early surgery in selected puppies can prevent some cases of degenerative joint disease. Surgery is also indicated for dogs who continue to experience pain and lameness despite medical treatment.

Five surgical options are available. Technical factors govern the choice. Triple pelvic osteotomy and femoral osteotomy are two operations performed on puppies that do not have degenerative joint changes. The goal of both operations is to position the femoral head more deeply in the acetabulum. Normal joint function is maintained with these operations and arthritis may not develop, although this is variable.

Pectineus myectomy is a relatively simple operation in which all of the pectineus muscle is removed on both affected sides. This operation does not slow the progress of joint disease but does afford pain relief for some time.

Femoral head and neck excision arthroplasty is an effective operation for the relief of intractable hip pain. The head of the femur is removed, allowing a fibrous union to replace the ball-and-socket joint. The operation is usually reserved for dogs weighing less than 36 pounds.

Total hip replacement is the most effective procedure for dogs nine months and older that have disabling degenerative joint disease in one or both hips.

The operation removes the old joint and replaces it with a new, artificial joint. The procedure requires special equipment and is usually performed by an orthopedic specialist. Good results are obtained in more than 95 percent of cases.

Prevention:

Preventing excessive weight gain in puppy hood and keeping the puppy from placing undue stress on the hips will delay the onset of hip dysplasia in many dogs with a genetic predisposition. It may also lead to a less severe form of the disease. Puppies at risk for hip dysplasia should be fed a calorie-controlled diet.

Preventing hip dysplasia in a bloodline is based on selective breeding practices. Hip dysplasia is a moderately heritable condition. It is twice as common among littermates having one dysplastic parent. Experience shows that repeated selection of normal dogs for breeding stock significantly reduces the incidence of hip dysplasia in susceptible bloodlines.

Information on breed risk is available through the OFA and PennHip. In breeds where hip dysplasia is a particular problem, prospective puppy buyers are advised to check pedigrees for OFA, PennHip or GDC certifications, particularly for sires and dams.